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/*
* GCM Mode
* (C) 2013 Jack Lloyd
*
* Distributed under the terms of the Botan license
*/
#ifndef BOTAN_AEAD_GCM_H__
#define BOTAN_AEAD_GCM_H__
#include <botan/aead.h>
#include <botan/block_cipher.h>
#include <botan/stream_cipher.h>
#include <memory>
namespace Botan {
class GHASH;
/**
* GCM Mode
*/
class BOTAN_DLL GCM_Mode : public AEAD_Mode
{
public:
secure_vector<byte> start(const byte nonce[], size_t nonce_len) override;
void set_associated_data(const byte ad[], size_t ad_len) override;
std::string name() const override;
size_t update_granularity() const;
Key_Length_Specification key_spec() const override;
// GCM supports arbitrary nonce lengths
bool valid_nonce_length(size_t) const override { return true; }
size_t tag_size() const { return m_tag_size; }
void clear();
protected:
void key_schedule(const byte key[], size_t length) override;
GCM_Mode(BlockCipher* cipher, size_t tag_size);
const size_t BS = 16;
const size_t m_tag_size;
const std::string m_cipher_name;
std::unique_ptr<StreamCipher> m_ctr;
std::unique_ptr<GHASH> m_ghash;
};
/**
* GCM Encryption
*/
class BOTAN_DLL GCM_Encryption : public GCM_Mode
{
public:
/**
* @param cipher the 128 bit block cipher to use
* @param tag_size is how big the auth tag will be
*/
GCM_Encryption(BlockCipher* cipher, size_t tag_size = 16) :
GCM_Mode(cipher, tag_size) {}
size_t output_length(size_t input_length) const override
{ return input_length + tag_size(); }
size_t minimum_final_size() const override { return 0; }
void update(secure_vector<byte>& blocks, size_t offset = 0) override;
void finish(secure_vector<byte>& final_block, size_t offset = 0) override;
};
/**
* GCM Decryption
*/
class BOTAN_DLL GCM_Decryption : public GCM_Mode
{
public:
/**
* @param cipher the 128 bit block cipher to use
* @param tag_size is how big the auth tag will be
*/
GCM_Decryption(BlockCipher* cipher, size_t tag_size = 16) :
GCM_Mode(cipher, tag_size) {}
size_t output_length(size_t input_length) const override
{
BOTAN_ASSERT(input_length > tag_size(), "Sufficient input");
return input_length - tag_size();
}
size_t minimum_final_size() const override { return tag_size(); }
void update(secure_vector<byte>& blocks, size_t offset = 0) override;
void finish(secure_vector<byte>& final_block, size_t offset = 0) override;
};
/**
* GCM's GHASH
* Maybe a Transform?
*/
class BOTAN_DLL GHASH : public SymmetricAlgorithm
{
public:
void set_associated_data(const byte ad[], size_t ad_len);
secure_vector<byte> nonce_hash(const byte nonce[], size_t len);
void start(const byte nonce[], size_t len);
/*
* Assumes input len is multiple of 16
*/
void update(const byte in[], size_t len);
secure_vector<byte> final();
Key_Length_Specification key_spec() const { return Key_Length_Specification(16); }
void clear();
std::string name() const { return "GHASH"; }
private:
void key_schedule(const byte key[], size_t key_len) override;
void gcm_multiply(secure_vector<byte>& x) const;
void ghash_update(secure_vector<byte>& x,
const byte input[], size_t input_len);
void add_final_block(secure_vector<byte>& x,
size_t ad_len, size_t pt_len);
secure_vector<byte> m_H;
secure_vector<byte> m_H_ad;
secure_vector<byte> m_nonce;
secure_vector<byte> m_ghash;
size_t m_ad_len = 0, m_text_len = 0;
};
}
#endif
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